Rubber composition and tire using the same as well as modified conjugated diene-based polymer and method for producing the same

ABSTRACT

This invention relates to a rubber composition being excellent in the low heat buildup and fracture properties (resistance to crack growth). and more particularly to a rubber composition, characterized by compounding 10-100 parts by mass of an inorganic filler and/or carbon black based on 100 parts by mass of a rubber component including not less than 10 mass % of a modified conjugated diene-based polymer having a cis-1,4 bond content of not less than 90% and a vinyl bond content of not more than 1.2% and a primary amino group. In this case, the modified conjugated diene-based polymer is obtained by (1) reacting the predetermined conjugated diene-based polymer having an active terminal with a compound having two or more predetermined functional groups and (2) further reacting the resulting product with a compound having a primary amino group.

This is a divisional of application Ser. No. 12/921,536, filed Dec. 8,2010, which is a 371 of PCT/JP2009/054556, filed Mar. 10, 2009, whichclaims priority from Japanese Patent Application No. 2008-059890, filedMar. 10, 2008, and Japanese Patent Application No. 2008-205812, filedAug. 8, 2008, the contents of which are hereby incorporated by referenceinto this application.

TECHNICAL FIELD

This invention relates to a modified conjugated diene-based polymer anda method of producing the same as well as a rubber composition and atire using such a polymer, and more particularly to a rubber compositionbeing excellent in the low heat buildup and fracture properties(resistance to crack growth).

RELATED ART

Recently, tires having a low rolling resistance are required in order tosave fuel consumption of an automobile under social demand for energysaving and resource saving, and hence a rubber composition beingexcellent in the low heat buildup (low loss factor) and fractureproperties as compared with the conventional ones is desired. In orderto reduce the rolling resistance of the tire, it is common to use arubber composition having a low heat buildup. Particularly, the use of apolymer introduced with a functional group interacting with a filler ina rubber composition as a rubber component is a very effective means.For instance, it is investigated to apply a modified high-cispolybutadiene rubber or the like introduced with a functional groupinteracting with the filler to a rubber composition (WO 2006/112450brochure).

In a high-cis polybutadiene rubber produced by coordinationpolymerization under industrial conditions, however, the reactivity of amodifier to a polymer terminal is low, so that the introduction of afunctional group having a high affinity with a filler can be onlyattained at a reaction efficiency of about 30% to total polymerterminal. Therefore, when the high-cis polybutadiene rubber is used, itis difficult to improve low loss factor of the rubber composition. Onthe other hand, in an anion polymerization system capable of introducinga functional group having a high affinity with a filler at a reactionefficiency of approximately 100% to a polymer terminal, the low lossfactor of the rubber composition can be largely improved, but it isconfirmed that the fracture properties are low as compared with a rubbercomposition compounded with an unmodified high-cis polybutadiene rubberobtained in the coordination polymerization system.

Moreover, it is known that the modified high-cis polybutadiene rubberintroduced with a functional group interacting with the filler issuperior in the fracture properties to the unmodified high-cispolybutadiene rubber, and hence modified high-cis polybutadiene rubberscapable of improving low loss factor of a rubber composition aredesired.

DISCLOSURE OF THE INVENTION

As mentioned above, the modified high-cis polybutadiene rubberintroduced with the functional group interacting with the fillerimproves the low loss factor and fracture properties of the rubbercomposition, so that a certain measure of successful results is broughtby serious studies and developments. However, the reaction efficiencybetween the polymer terminal and the modifying agent is still low, andthere is a limit for improving the low loss factor by increasing thereaction efficiency.

The inventors have made investigations on functional groups to beintroduced into a polymer terminal and found that the low loss factorcan be improved to a new level by introducing an amino group with activehydrogen having a very high affinity with carbon black into a polymerterminal. As a result of further investigations, it has been found thatthe introduction of a primary amino group into a polymer terminal issignificant in the low loss factor as compared with the introduction ofa secondary amino group or a tertiary amino group.

It is, therefore, an object of the invention to provide a modifiedconjugated diene-based polymer capable of improving low heat buildup andfracture properties (resistance to crack growth) of a rubber compositionand a method of producing such a modified conjugated diene-basedpolymer. Also, it is another object of the invention to provide a rubbercomposition using the modified conjugated diene-based polymer as arubber component as well as a tire using such a rubber composition.

The inventors have made various studies in order to achieve the aboveobjects and discovered that a modified conjugated diene-based polymerhaving specified cis-1,4 bond content and vinyl bond content and aprimary amino group is obtained by (1) reacting a compound having two ormore predetermined functional groups with a given conjugated diene-basedpolymer having an active terminal and (2) further reacting the resultingproduct with a compound having a primary amino group, and that low heatbuildup and fracture properties can be largely improved by applying arubber composition using the modified conjugated diene-based polymer asa rubber component and further compounding a specified filler to a tire,and as a result, the invention has been accomplished.

That is, the rubber composition according to the invention ischaracterized by compounding 10-100 parts by mass of an inorganic fillerand/or carbon black based on 100 parts by mass of a rubber componentincluding not less than 10 mass % of a modified conjugated diene-basedpolymer having a cis-1,4 bond content of not less than 90% and a vinylbond content of not more than 1.2% and a primary amino group.

Moreover, the cis-1,4 bond content means a ratio of cis-1,4 bond in aconjugated diene compound unit of the polymer, and the vinyl bondcontent means a ratio of vinyl bond in the conjugated diene compoundunit of the polymer.

In the rubber composition according to the invention, the modifiedconjugated diene-based polymer is preferable to have a vinyl bondcontent of not more than 0.8%.

In the rubber composition according to the invention, carbon black ispreferable to have a nitrogen adsorption specific surface area of 20-180m²/g, more preferably 20-100 m²/g.

In a preferable embodiment of the rubber composition according to theinvention, the rubber component comprises 10-90 mass % of the modifiedconjugated diene-based polymer and 90-10 mass % of a diene-based polymerother than the modified conjugated diene-based polymer. In this case,the diene-based polymer other than the modified conjugated diene-basedpolymer is preferable to be natural rubber.

The rubber composition according to the invention is preferable to besulfur cross-linkable.

Also, the tire according to the invention is characterized by using theabove-mentioned rubber composition in any tire member.

Further, the method of producing the modified conjugated diene-basedpolymer according to the invention is characterized by comprising:

(1) a step of reacting a conjugated diene-based polymer having a cis-1,4bond content of not less than 90% and a vinyl bond content of not morethan 1.2% and an active terminal with a compound X having a functionalgroup A indicating a reactivity to the active terminal and at least onereactive functional group B (provided that the functional group A andthe functional group B may be same) to obtain a primary modifiedconjugated diene-based polymer; and

(2) a step of reacting the primary modified conjugated diene-basedpolymer with a compound Y having a functional group C indicating areactivity to the reactive functional group B and at least one primaryamino group or protected primary amino group (provided that thefunctional group C may be the primary amino group or the protectedprimary amino group) to obtain a secondary modified conjugateddiene-based polymer.

In the production method of the modified conjugated diene-based polymeraccording to the invention, the conjugated diene-based polymer ispreferable to have a vinyl bond content of not more than 0.8%.

In a preferable embodiment, the production method of the modifiedconjugated diene-based polymer according to the invention furthercomprises (3) a step of hydrolyzing the secondary modified conjugateddiene-based polymer to deprotect the protected primary amino groupderived from the compound Y.

In another preferable embodiment of the production method of themodified conjugated diene-based polymer according to the invention, theconjugated diene-based polymer is synthesized with a rare earth metal asa catalyst.

In the other preferable embodiment of the production method of themodified conjugated diene-based polymer according to the invention, thecompound X is polymethylene polyphenyl polyisocyanate, and the compoundY is hexamethylene diamine.

Moreover, the modified conjugated diene-based polymer according to theinvention is characterized by producing through the above method.

According to the invention, there can be provided a modified conjugateddiene-based polymer having specified cis-1,4 bond content and vinyl bondcontent and a primary amino group and capable of giving low heat buildupand fracture properties (resistance to crack growth) to a rubbercomposition and a method of producing the modified conjugateddiene-based polymer by (1) reacting a given conjugated diene-basedpolymer having a compound having two or more given functional groups and(2) reacting the resulting product with a compound having a primaryamino group. In addition, there can be provided a rubber compositionhaving excellent low heat buildup and fracture properties (resistance tocrack growth) and a tire by using the above modified conjugateddiene-based polymer.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in detail below. The rubber compositionaccording to the invention is characterized by compounding 10-100 partsby mass of an inorganic filler and/or carbon black based on 100 parts bymass of a rubber component containing not less than 10 mass % of amodified conjugated diene-based polymer having a cis-1,4 bond content ofnot less than 90%, a vinyl bond content of not more than 1.2% and aprimary amino group. At this moment, the modified conjugated diene-basedpolymer used as the rubber component in the rubber composition accordingto the invention is a polymer indicating a stretching crystallinitybecause the cis-1,4 bond content is not less than 90% and the vinyl bondcontent is not more than 1.2%. Also, the modified conjugated diene-basedpolymer is generally low in the reaction efficiency to a modifyingagent. However, the modified conjugated diene-based polymer used as arubber component in the rubber composition according to the invention isvery high in the affinity with a filler such as inorganic filler, carbonblack or the like due to the introduction of the primary amino group,and can disperse the filler effectively even in the reaction efficiency.Therefore, the rubber composition according to the invention improvesthe fracture properties owing to the stretching crystallinity of themodified conjugated diene-based polymer and can largely improve the lowheat buildup because the dispersibility of the filler is furtherimproved. Moreover, the production method of the modified conjugateddiene-based polymer used as a rubber component in the rubber compositionaccording to the invention will be described in detail below.

The rubber component in the rubber composition according to theinvention is required to include not less than 10 mass % of the modifiedconjugated diene-based polymer. When the ratio of the modifiedconjugated diene-based polymer included in the rubber component is lessthan 10 mass %, the effect of improving the dispersibility of the fillerbecomes particularly small and the low heat buildup of the rubbercomposition is not obtained sufficiently. In the rubber compositionaccording to the invention, the modified conjugated diene-based polymermay be used by combining with a rubber component other than the modifiedconjugated diene-based polymer. As the rubber component (diene-basedpolymer) other than the modified conjugated diene-based polymer arementioned natural rubber (NR), polyisoprene rubber (IR),styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR),ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR),halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR) and soon, and among them natural rubber is preferable. These rubber componentsother than the modified conjugated diene-based polymer may be used aloneor in a blend of two or more. Moreover, when the modified conjugateddiene-based polymer is combined with the diene-based polymer such asnatural rubber or the like other than the modified conjugateddiene-based polymer, the rubber component is preferable to comprise10-90 mass % of the modified conjugated diene-based polymer and 90-10mass % of the diene-based polymer other than the modified conjugateddiene-based polymer.

In the rubber composition according to the invention, the inorganicfiller and/or carbon black is compounded in an amount of 10-100 parts bymass based on 100 parts by mass of the rubber component as a filler.When the amount of the inorganic filler and/or carbon black compoundedis less than 10 parts by mass, the fracture properties of the rubbercomposition are deteriorated, while when it exceeds 100 parts by mass,the low heat buildup of the rubber composition may be deteriorated.

The carbon black is not particularly limited, but is preferable to havea nitrogen adsorption specific surface area of 20-180 m²/g, morepreferably 20-100 m²/g. When the carbon black has a nitrogen adsorptionspecific surface area of 20-180 m²/g, the particle size is large and theeffect of improving the low heat buildup is very high. As the carbonblack are concretely preferable grades of not more than HAF, whichinclude, for example, HAF, FF, FEF, GPF, SRF, FT grades. From viewpointof the fracture properties, HAF, FEF and GPF grades are particularlypreferable. As the inorganic filler are mentioned silica, talc, aluminumhydroxide and so on. Moreover, these fillers may be used alone or in acombination of two or more.

The rubber composition according to the invention can be produced bycompounding the rubber component with the inorganic filler and/or carbonblack and additives usually used in the rubber industry and properlyselected from a softening agent, stearic acid, an antioxidant, zincoxide, a vulcanization accelerator, a vulcanizing agent and so onwithout damaging the object of the invention, and milling, warming,extruding them.

Moreover, the rubber composition according to the invention ispreferable to be sulfur cross-linkable, and it is preferable to usesulfur or the like as a vulcanizing agent. The amount of the vulcanizingagent used is preferably 0.1-10.0 parts by mass, more preferably 1.0-5.0parts by mass based on 100 parts by mass of the rubber component as asulfur amount.

Also, the tire according to the invention is characterized by using theabove rubber component in a tire member. As the tire member arementioned, for example, a tire tread, an under-tread, a carcass, asidewall, a bead portion and the like. Moreover, the tire according tothe invention is obtained by using the rubber composition at an uncuredstate to form tire members, forming a green tire therefrom according toa usual manner, and vulcanizing the green tire. The tire obtained byapplying the rubber composition to any tire member is excellent in thefracture properties (resistance to crack growth) and low heat buildup.As a gas to be filled in the tire may be used common air or air havingan adjusted partial oxygen pressure as well as an inert gas such asnitrogen, argon, helium or the like.

The modified conjugated diene-based polymer according to the inventionand the production method thereof will be described in detail below. Themethod of producing the modified conjugated diene-based polymeraccording to the invention is characterized by comprising (1) a step ofreacting a conjugated diene-based polymer having a cis-1,4 bond contentof not less than 90% and a vinyl bond content of not more than 1.2% andan active terminal with a compound X having a functional group Aindicating a reactivity to the active terminal and at least one reactivefunctional group B (provided that the functional group A and thefunctional group B may be same) to obtain a primary modified conjugateddiene-based polymer (primary modification reaction); and (2) a step ofreacting the primary modified conjugated diene-based polymer with acompound Y having a functional group C indicating a reactivity to thereactive functional group B and at least one primary amino group orprotected primary amino group (provided that the functional group C maybe the primary amino group or the protected primary amino group) toobtain a secondary modified conjugated diene-based polymer (secondarymodification reaction), and may further comprise (3) a step ofhydrolyzing the secondary modified conjugated diene-based polymer todeprotect the protected primary amino group derived from the compound Y(deprotection reaction), if necessary.

The modified conjugated diene-based polymer obtained through the steps(1) and (2) or the modified conjugated diene-based polymer obtainedthrough the steps (1), (2) and (3) has a cis-1,4 bond content of notless than 90%, a vinyl bond content of not more than 1.2% and a primaryamino group, so that it can be used as a modified conjugated diene-basedpolymer in the rubber composition, and hence the fracture properties andlow heat buildup of the rubber composition are improved largely.Moreover, the compound having a reactivity with the active terminal ofthe conjugated diene-based polymer and a primary amino group is notcommercially available and also it is difficult to introduce the primaryamino group into the conjugated diene-based polymer, so that doublemodification reaction (primary modification reaction and secondarymodification reaction) for obtaining the modified conjugated diene-basedpolymer is carried out in the production method according to theinvention.

The modified conjugated diene-based polymer according to the inventionis required to have a cis-1,4 bond content of not less than 90%. Whenthe cis-1,4 bond content is less than 90%, the low loss factor in therubber composition can not be obtained sufficiently. Also, the modifiedconjugated diene-based polymer according to the invention is required tohave a vinyl bond content of not more than 1.2%. When the vinyl bondcontent exceeds 1.2%, the crystallinity of the polymer is deteriorated.

Furthermore, the modified conjugated diene-based polymer according tothe invention has a primary amino group or a protected primary aminogroup in its molecule. Thus, when the modified conjugated diene-basedpolymer according to the invention has the primary amino group in itsmolecule, the polymer is directly used as a rubber component, while whenthe modified conjugated diene-based polymer according to the inventionhas the protected primary amino group in its molecule, the polymerdeprotected through the above step (3) is used as a rubber component,whereby the low heat buildup of the resulting rubber composition can beimproved largely.

In addition, the number average molecular weight of the modifiedconjugated diene-based polymer according to the invention is notparticularly limited, which does not cause a problem of decreasing themolecular weight in a production process mentioned later. Furthermore,the molecular weight distribution represented by a ratio of weightaverage molecular weight (Mw) to number average molecular weight (Mn) ispreferably not more than 3.5, more preferably not more than 3.0, mostpreferably not more than 2.5. At this moment, the average molecularweight and molecular weight distribution can be determined by a gelpermeation chromatography (GPC) using polystyrene as a standardsubstance.

Moreover, the Mooney viscosity [ML₁₊₄ (100° C.)] of the modifiedconjugated diene-based polymer according to the invention is preferably10-100, more preferably 20-80. When the Mooney viscosity [ML₁₊₄ (100°C.)] is less than 10, there is a tendency of deteriorating the rubberproperties inclusive of fracture properties, while when it exceeds 100,the processability is deteriorated, and the milling with additives maybe difficult.

In the production of the modified conjugated diene-based polymeraccording to the invention, it is first required to obtain a primarymodified conjugated diene-based polymer through the step (1).

The conjugated diene-based polymer used in the step (1) has a cis-1,4bond content of not less than 90%, a vinyl bond content of not more than1.2% and an active terminal. The production method of such a conjugateddiene-based polymer is not particularly limited, and may use aproduction method using the conventionally well-known polymerizationreaction, but a production method using a coordination polymerization ispreferable. Also, when a solvent is used in the polymerization reaction,such a solvent may be inactive in the polymerization reaction andincludes, for example, butane, pentane, hexane, heptane, cyclopentane,cyclohexane, 1-butene, 2-butene, benzene, toluene, xylene, methylenechloride, chloroform, carbon tetrachloride, trichloroethylene,perchloroethylene, 1,2-dichloroethane, chlorobenzene, bromobenzene,chlorotoluene and so on. Furthermore, the temperature of thepolymerization reaction is preferably a range of −30° C-200° C., morepreferably a range of 0° C.-150° C. In addition, it is preferable totake a care that the incorporation of a compound having a deactiveaction such as oxygen, water, carbon dioxide gas or the like into thepolymerization system is removed as far as possible in order not todeactivate the active terminal of the conjugated diene-based polymerproduced. Moreover, the polymerization system is not particularlylimited, and may be a batch type or a continuous type.

The conjugated diene-based polymer is preferable to be a homopolymer ofa conjugated diene compound or a copolymer of an aromatic vinyl compoundand a conjugated diene compound. As the conjugated diene compound beinga monomer are mentioned 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene, myrceneand the like, and among them 1,3-butadiene and isoprene are preferable.On the other hand, as the aromatic vinyl compound being a monomer arementioned styrene, p-methylstyrene, m-methylstyrene,p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, vinyl tolueneand the like.

The conjugated diene-based polymer is preferable to be synthesized witha rare earth metal as a catalyst, and is obtained, for example, bypolymerizing the monomer(s) in the presence of a polymerization catalystcomposition comprising the following components (a)-(c) as a maincomponent.

Component (a): a lanthanoid element-containing compound containing atleast one of lanthanoid elements (rare earth elements corresponding toatomic numbers of 57-71 in the Periodic Table) or a reaction productobtained by reacting the lanthanoid element-containing compound with aLewis base

Component (b): alumoxane and/or an organoaluminum compound representedby a general formula (I): AlR¹R²R³ (in the general formula (I), R¹ andR² may be same or different and are a hydrocarbon group having a carbonnumber of 1-10 or a hydrogen atom, and R³ may be same as or differentfrom R¹ and R² and is a hydrocarbon group having a carbon number of1-10)

Component (c): a halogen-containing compound containing at least onehalogen element in its molecule

By polymerizing with such a catalyst to produce a conjugated diene-basedpolymer can be obtained a conjugated diene-based polymer having a narrowmolecular weight distribution and a high cis-1,4 bond content. Also,this catalyst (catalyst composition) is cheap as compared with theconventional metallocene catalyst but also has not a requirement thatthe polymerization reaction is carried out at an extremely lowtemperature. Therefore, the operation is simple and is useful as anindustrially production process.

The component (a) used in the polymerization catalyst composition is alanthanoid element-containing compound containing at least one oflanthanoid elements (rare earth elements corresponding to atomic numbersof 57-71 in the Periodic Table) or a reaction product obtained byreacting the lanthanoid element-containing compound with a Lewis base.As a concrete example of the lanthanoid element may be mentionedneodymium, praseodymium, cerium, lanthanum, gadolinium, samarium and thelike. Among them, neodymium is preferable. Moreover, these lanthanoidelements may be used alone or in a combination of two or more. As aconcrete example of the lanthanoid element-containing compound may bementioned carboxylates, alkoxides, β-diketone complexes, phosphates,phosphites and the like of these lanthanoid elements. Among them,carboxylates or phosphates are preferable, and further carboxylates arepreferable.

As the carboxylate of the lanthanoid element are preferably mentionedsalts of 2-hexylhexane, naphthenic acid, versatic acid [trade name, madeby Shell Chemicals Co., Ltd. carboxylic acid having a carboxyl groupbonded to a tertiary carbon atom) and the like. As a concrete example ofthe alkoxide of the lanthanoid element may be mentioned a compoundrepresented by a general formula (II): (R⁴O)₃M (in the general formula(II), M is a lanthanoid element, and R⁴ is a hydrocarbon group having acarbon number of 1-20). As an alkoxy group represented by “R⁴O” in theformula (II), are preferably mentioned 2-ethyl-hexylalkoxy group,benzylalkoxy group and the like. As the β-diketone complex of thelanthanoid element are preferably mentioned acetylacetone complex,ethylacetylacetone complex and the like. As the phosphate or phosphiteof the lanthanoid element are preferably mentionedbis(2-ethylhexyl)phosphate, bis(1-methylheptyl)phosphate, 2-ethylhexylphosphonic acid mono-2-ethylhexyl, bis(2-ethylhexyl)phosphinic acid andthe like.

Among the above-mentioned ones, phosphate of neodymium or carboxylate ofneodymium is further preferable as the lanthanoid element-containingcompound, and the carboxylate such as neodymium 2-ethylhexanoate,neodymium versatate or the like is particularly preferable.

In order to solubilize the lanthanoid element-containing compound in asolvent or store stably for a long time, it is also preferable to mixthe lanthanoid element-containing compound with a Lewis base or reactthe lanthanoid element-containing compound with a Lewis base to form areaction product. The amount of the Lewis base is preferably 0-30 mol,more preferably 1-10 mol per 1 mol of the lanthanoid element. As aconcrete example of the Lewis base may be mentioned acetylacetone,tetrahydrofuran, pyridine, N,N-dimethylformamide, thiophene, diphenylether, triethylamine, an organophosphorus compound, a monovalent ordivalent alcohol and the like. The above-mentioned components (a) may beused alone or in a combination of two or more.

The component (b) used in the polymerization catalyst composition isalumoxane and/or an organoaluminum compound represented by the generalformula (I). Alumoxane (which is also called as aluminoxane) is acompound of a structure represented by the following general formula(III) or (IV). Moreover, it may be an association body of alumoxanedisclosed in Fine Chemical, 23, (9), 5 (1994), J. Am. Chem. Soc., 115,4971 (1993) and J. Am. Chem. Soc., 117, 6465 (1995).

In the general formulae (III) and (IV), R⁵ is a hydrocarbon group havinga carbon number of 1-20, which includes concretely methyl group, ethylgroup, propyl group, butyl group, isobutyl group, t-butyl group, hexylgroup, isohexyl group, octyl group, isooctyl group and the like. Amongthem, methyl group is particularly preferable. n′ is an integer of notless than 2, and is preferable to be an integer of 4-100.

As a concrete example of alumoxane may be mentioned methylalumoxane(MAO), ethylalumoxane, n-propylalumoxane, n-butylalumoxane,isobutylalumoxane, t-butylalumoxane, hexylalumoxane, isohexylalumoxaneand the like. Alumoxane can be produced by a well-known method. Forexample, it can be produced by adding trialkyl aluminum or dialkylaluminum chloride to an organic solvent such as benzene, toluene, xyleneor the like, further adding water, steam, steam-containing nitrogen gas,or a salt containing water of crystallization such as 6 hydrate ofcopper sulfate, 16 hydrate of aluminum sulfate or the like to conductthe reaction. Moreover, the alumoxanes may be used alone or in acombination of two or more.

As a concrete example of the organoaluminum compound represented by thegeneral formula (I) may be mentioned triethyl aluminum, triisobutylaluminum, hydrogenated diethyl aluminum, hydrogenated diisobutylaluminum and the like. Moreover, the organoaluminum compounds may beused alone or in a combination of two or more.

The component (c) used in the polymerization catalyst composition is ahalogen-containing compound containing at least one halogen element inits molecule, and may preferably include, for example, a reactionproduct between a metal halide and a Lewis base, diethylaluminumchloride, silicon tetrachloride, trimethylchlorosilane,methyldichlorosilane, dimethyldichlorosilane, methyltrichlorosilane,ethylaluminum dichloride, ethylaluminum sesquichloride, tintetrachloride, tin trichloride, phosphorus trichloride, benzoylchloride, t-butyl chloride, trimethylsilyl iodide, triethylsilyl iodide,dimethylsilyl diiode, diethylaluminum iodide, methyl iodide, butyliodide, hexyl iodide, octyl iodide, iodoform, diiodomethane, iodine,benzylidene iodide and the like.

As the metal halide usable in the reaction product between the metalhalide and Lewis base are mentioned magnesium chloride, manganesechloride, zinc chloride, magnesium iodide, manganese iodide, zinciodide, copper iodide and the like. As the Lewis base may be preferablyused a phosphorus compound, a carbonyl compound, a nitrogen compound, anether compound, an alcohol and so on. Concretely, there may bepreferably mentioned tri-2-ethylhexyl phosphate, tricresyl phosphate,acetylacetone, 2-ethylhexanoic acid, versatic acid, 2-ethylhexylalcohol, 1-decanol, lauryl alcohol and the like. The Lewis base ispreferably reacted at a ratio of 0.01 mol-30 mol, more preferably 0.5mol-10 mol per 1 mol of the metal halide. When the reaction product withthe Lewis base is used, metal(s) remaining in the polymer can bereduced.

Moreover, the compounding ratio of the components (a)-(c) as a maincomponent of the catalyst may be properly set, if necessary. The amountof the component (a) used is preferably 0.00001 mmol-1.0 mmol, morepreferably 0.0001 mmol-0.5 mmol per 100 g of the monomer.

When the component (b) is alumoxane, the preferable amount of thealumoxane included in the catalyst can be represented by a molar ratioof component (a) to aluminum (Al) included in the alumoxane. That is, amolar ratio of “component (a)” to aluminum (Al) included in alumoxane ispreferably 1:1-1:500, more preferably 1:3-1:250, particularly preferably1:5-1:200. On the other hand, when the component (b) is anorganoaluminum compound, the preferable amount of the organoaluminumcompound included in the catalyst can be represented by a molar ratio ofcomponent (a) to organoaluminum compound. That is, the molar ratio of“component (a)” to “organoaluminum compound” is preferably 1:1-1:700,more preferably 1:3-1:500.

Also, the preferable amount of the component (c) included in thecatalyst composition can be represented by a molar ratio of a halogenatom included in the component (c) to component (a). That is, the molarratio of (halogen atom)/(component (a)) is preferably 20-0.1, morepreferably 15-0.2, particularly preferably 8-0.5.

The catalyst may be previously prepared by using the same conjugateddiene compound and/or non-conjugated diene compound as in the monomerfor polymerization in addition to the above components (a)-(c).

The catalyst composition may be prepared, for example, by reacting thecomponents (a)-(c) dissolved in a solvent and, if necessary, aconjugated diene compound and/or non-conjugated diene compound added.Moreover, the addition order of the components is optional. However, itis preferable that the components are mixed and reacted and then maturedfrom a viewpoint of improvement of polymerization activity, andshortening of induction period for the start of polymerization. Thematuring temperature is preferably 0° C-100° C., more preferably 20°C-80° C. Moreover, the maturing time is not particularly limited. Thecomponents may be contacted with each other in a line before theaddition to a polymerization reaction vessel. The maturing time issufficient to be not less than 0.5 minute. Also, the prepared catalystcomposition is stable for several days.

By using such a catalyst (catalyst composition) can be obtained aconjugated diene-based polymer having a cis-1,4 bond content of not lessthan 90%, a vinyl bond content of not more than 1.2% and an activeterminal. Moreover, the cis-1,4 bond content and vinyl bond content canbe adjusted easily by controlling the polymerization temperature.

In the step (1), the conjugated diene-based polymer having the activesite is reacted with a compound X, whereby there is obtained a primarymodified conjugated diene-based polymer in which the compound X isintroduced into the active terminal of the conjugated diene-basedpolymer.

The compound X used in the step (1) is a compound having a functionalgroup A indicating the reactivity to the active terminal of theconjugated diene-based polymer and at least one reactive functionalgroup B. At this moment, the functional group A and the functional groupB may be same or different and include, for example, ketene group,isocyanate group, thioisocyanate group, carboimide group and so on.

As the compound X are preferably mentioned 4,4′-diphenylmethanediisocyanate, polymethylene polyphenyl polyisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, 1,6-hexamethylene diisocyanate,4,4′-dicyclohexylmethane diisocyanate, isopropylidenebis(4-cyclohexylisocyanate), xylylene diisocyanate,3,3′-dimethyl-4,4′-biphenyl diisocyanate, 3,3′-dimethoxy-4,4′-biphenyldiisocyanate, 3,3′-dimethyl-4,4′-diphenylmethane diisocyanate,1,5-naphthalene diisocyanate, bis(2-isocyanateethyl)fumarate,2,4-tolylenedithio isocyanate, 4,4′-diphenylmethanedithio isocyanate,1,6-hexamethylenedithio isocyanate and so on. In the production methodof the modified conjugated diene-based polymer according to theinvention, a heterocumulene compound having two or more isocyanategroups is preferably used as the compound X, and the use ofpolymethylene polyphenyl polyisocyanate is particularly preferable.Moreover, the compounds X may be used alone or in a combination of twoor more.

The amount of the compound X used is preferably 0.02 mmol-20 mmol, morepreferably 0.1 mmol-10 mmol, particularly preferably 0.2 mmol-5 mmol per100 g of the monomer. When the amount of the compound X used is lessthan 0.02 mmol, primary modification reaction does not proceedsufficiently, and the functional group reacting with a compound Y maynot be introduced sufficiently into the conjugated diene-based polymer,while when it exceeds 20 mmol, the number of functional groups reactingwith a compound Y in the conjugated diene-based polymer is saturated andis not preferable in economical reasons.

The primary modification reaction is preferable to be conducted bysolution reaction. The solution in this reaction may be a solutioncontaining an unreatced monomer used, for example, in the polymerizationof the conjugated diene-based polymer. The primary modification reactionsystem is not particularly limited and may be conducted by using a batchtype reactor or may be continuous type using an apparatus such as amultistage continuous reactor, an in-line mixer or the like. Moreover,the primary modification reaction is important to be carried out afterthe completion of the polymerization reaction and before variousoperations required for desolvation treatment, water treatment, heattreatment and polymer isolation.

As the temperature of the primary modification reaction can be used thepolymerization temperature of the conjugated diene-based polymer itself.Concretely, it is preferably 0° C.-120° C., more preferably 10° C.-100°C. As the temperature becomes lower, it tends to raise the viscosity ofthe resulting polymer (primary modified conjugated diene-based polymer),while as the temperature becomes higher, the active terminal of thepolymer is easily deactivated. Also, the tire required for the primarymodification reaction is preferably 5 minutes-5 hours, more preferably15 minutes-1 hour.

In the primary modification reaction, the active terminal of theconjugated diene-based polymer is reacted with the functional group A ofthe compound X to provide a primary modified conjugated diene-basedpolymer. In order to further react with the compound Y in the followingsecondary modification reaction (step (2)), however, it is necessarythat at least one of functional groups B in the compound X is left at anunreacted state.

Subsequently, in order to produce the modified conjugated diene-basedpolymer according to the invention, it is required to provide asecondary modified conjugated diene-based polymer through the step (2).In the step (2), the primary modified conjugated diene-based polymerobtained in the step (1) is reacted with the compound Y, whereby therecan be obtained a secondary modified conjugated diene-based polymer inwhich the compound y is introduced into the reactive functional group Bderived from the compound X.

The compound Y used in the step (2) is a compound having a functionalgroup C indicating the reactivity to the reactive functional group Bderived from the compound X and at least one primary amino group orprotected primary amino group. As the functional group C are mentionedamino group, imino group, mercapto group, hydroxyl group and the like.Moreover, the functional group C may be a primary amino group or aprotected primary amino group.

As the compound Y are preferably mentioned hexamethylene diamine,heptamethylene diamine, nonamethylene diamine, dodecamethylene diamine,decamethylene diamine, 1,5-naphthalene diamine, 1,8-naphthalene diamine,1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane,ethylene diamine, diethylene triamine, triethylene tetramine,tetraethylene pentamine, pentaethylene hexamine and so on.

When the compound Y has a protected primary amino group, for example, assuch a compound Y are preferably mentioned hexamethyl disilazane,N-chlorohexamethyl disilazane, N-bromohexamethyl disilazane,1-(3-bromopropyl)-2,2,5,5-tetramethyl-1-aza-2,5-dicyacyclopentane,1-(3-chloropropyl)-2,2,5,5-tetramethyl-1-aza-2,5-dicyacyclopentane andthe like.

The secondary modification reaction may be successively conducted withthe above primary modification reaction, which is preferable to beconducted by a solution reaction likewise the primary modificationreaction. The solution in this reaction may be a solution containing anunreacted monomer used, for example, in the polymerization of theconjugated diene-based polymer. Also, the secondary modificationreaction system is not particularly limited, and may be conducted byusing a batch type reactor or may be continuous type using an apparatussuch as a multistage continuous reactor, an in-line mixer or the likelikewise the primary modification reaction. Moreover, the secondarymodification reaction is important to be carried out after thecompletion of the polymerization reaction and before various operationsrequired for desolvation treatment, water treatment, heat treatment andpolymer isolation.

The amount of the compound Y used is preferably 0.02 mmol-20 mmol, morepreferably 0.1 mmol-10 mmol, particularly preferably 0.2 mmol-5 mmol per100 g of the monomer. When the amount of the compound Y used is lessthan 0.02 mmol, the secondary modification reaction does not proceedsufficiently, and the dispersibility with a filler is not developedsufficiently but also the effect of improving the fracture properties isnot developed, while when it exceeds 20 mmol, the dispersibility of thefiller and the effect of improving the properties are saturated and arenot preferable in economical reasons.

As the temperature of the secondary modification reaction may be usedthe temperature of the primary modification reaction itself. Concretely,it is preferably 0° C.-120° C., more preferably 10° C.-100° C. As thetemperature becomes lower, it tends to raise the viscosity of theresulting polymer (secondary modified conjugated diene-based polymer),while as the temperature becomes higher, the active terminal of thepolymer is easily deactivated. Also, the tire required for the secondarymodification reaction is preferably 5 minutes-5 hours, more preferably15 minutes-1 hour.

In the step (2), it is preferable to use a catalyst promoting thereaction between the functional group B derived from the compound X inthe primary modified conjugated diene-based polymer and the functionalgroup C of the compound Y (catalyst for addition reaction). Concretely,it is preferable to add a catalyst promoting the reaction between thefunctional group B derived from the compound X in the primary modifiedconjugated diene-based polymer and the functional group C of thecompound Y (catalyst for addition reaction) after the addition of thecompound X in the step (1) or after the addition of the compound Y inthe step (2). As such a catalyst for addition reaction can be used acompound having a tertiary amino group, or a compound containing one ormore elements belonging to any of Group 4A, Group 2B, Group 3B, Group 4Band Group 5B in the Periodic Table. A compound containing one or moreelements of titanium (Ti), zirconium (Zr), bismuth (Bi), aluminum (Al)and tin (Sn) is further preferable. It is particularly preferable thatthe compound constituting the catalyst is an alkoxide, a carboxylate oran acetylacetonate complex salt.

As the catalyst for addition reaction may be concretely mentionedtitanium-containing compounds such as tetramethoxytitanium,tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium,tetra-n-butoxytitanium, tetra-n-butoxytitanium oligomer,tetra-sec-butoxytitanium, tetra-tert-butoxytitanium,tetra(2-ethylhexyl)titanium,bis(octanedioleate)bis(2-ethylhexyl)titanium,tetra(octanedioleate)titanium, titanium lactate, titaniumdipropoxybis(triethanolaminate), titaniumdibutoxybis(triethanolaminate), titanium tributoxy stearate, titaniumtripropoxy stearate, titanium tripropoxy acetylacetonate, titaniumdipropoxybis(acetylacetonate), titanium tripropoxyethyl acetoacetate,titanium propoxyacetylacetonate bis(ethylacetylacetate), titaniumtributoxy acetylacetonate, titanium dibutoxybis(acetylacetonate),titanium tributoxyethyl acetoacetate, titanium butoxyacetylacetonatebis(ethylacetoacetate), titanium tetrakis(acetylacetonate), titaniumdiacetylacetonate bis(ethylacetoacetate), bis(2-ethylhexanoate)titaniumoxide, bis(laurate)titanium oxide, bis(naphthate)titanium oxide,bis(stearate)titanium oxide, bis(oleate)titanium oxide,bis(linorate)titanium oxide, tetrakis(2-ethylhexanoate)titanium,tetrakis(laurate)titanium, tetrakis(naphthate)titanium,tetrakis(stearate)titanium, tetrakis(oleate)titanium,tetrakis(linorate)titanium and so on.

Also, the catalyst for addition reaction may include, for example,tris(2-ethylhexanoate)bismuth, tris(laurate)bismuth,tris(naphthate)bismuth, tris(stearate)bismuth, tris(oleate)bismuth,tris(linorate)bismuth, tetraethoxyzirconium, tetra-n-propoxyzirconium,tetra-i-propoxyzirconium, tetra-n-butoxyzirconium,tetra-sec-butoxyzirconium, tetra-tert-butoxyzirconium,tetra(2-ethylhexyl)zirconium, zirconium tributoxystearate, zirconiumtributoxyacetylacetonate, zirconium dibutoxybis(acetylacetonate),zirconium trobutoxyethylacetoacetate, zirconium butoxyacetylacetonatebis(ethylacetoacetate), zirconium tetrakis(acetylacetonate), zirconiumdiacetylacetonate bis(ethylacetoacetate), bis(2-ethylhexanoate)zirconiumoxide, bis(laurate)zirconium oxide, bis(naphthate)zirconium oxide,bis(stearate)zirconium oxide, bis(oleate)zirconium oxide,bis(linorate)zirconium oxide, tetrakis(2-ethylhexanoate)zirconium,tetrakis(laurate)zirconium, tetrakis(naphthate)zirconium,tetrakis(stearate)zirconium, tetrakis(oleate)zirconium,tetrakis(linorate)zirconium and so on.

Further, the catalyst for addition reaction may include, for example,triethoxyaluminum, tri-n-propoxyaluminum, tri-i-propoxyaluminum,tri-n-butoxyaluminum, tri-sec-butoxyaluminum, tri-tert-butoxyaluminum,tri(2-ethylhexyl)aluminum, aluminum dibutoxystearate, aluminumdibutoxyacetylacetonate, aluminum butoxybis(acetylacetonate), aluminumdibutoxyethylacetoacetate, aluminum tris(acetylacetonate), aluminumtris(ethylacetoacetate), tris(2-ethylhexanoate)aluminum,tris(laurate)aluminum, tris(naphthate)aluminum, tris(stearate)aluminum,tris(oleate)aluminum, tris(linorate)aluminum and so on.

Moreover, the catalyst for addition reaction may includebis(n-octanoate)tin, bis(2-ethylhexanoate)tin, bis(laurate)tin,bis(naphthoenate)tin, bis(stearate)tin, bis(oleate)tin, dibutyltindiacetate, dibutyltin di-n-octanoate, dibutyltin di-2-ethylhexanoate,dibutyltin dilaurate, dibutyltin maleate, dibutyltin bis(benzylmaleate),dibutyltin bis(2-ethylhexylmaleate), di-n-octyltin diacetate,di-n-octyltin di-n-octanoate, di-n-octyltin di-2-ethylhexanoate,di-n-octyltin dilaurate, di-n-octyltin maleate, di-n-octyltinbis(benzylmaleate), di-n-octyltin bis(2-ethylhexylmaleate) and so on.

The amount of the catalyst for addition reaction used is preferably0.1-10, more preferably 0.5-5 as a molar ratio of mol number of thecompound exemplified as the catalyst to total of unreacted functionalgroup A and functional group B existing in the reaction system. When themolar ratio is less than 0.1, the modification reaction (concretely,secondary modification reaction) does not proceed sufficiently, whilewhen it exceeds 10, the effect as the catalyst for addition reaction issaturated and is not preferable in economic reasons.

The modified conjugated diene-based polymer according to the inventioncan be recovered by adding a shortstop or a polymerization stabilizer tothe reaction system, if necessary, after the completion of the step (1)and step (2) and then conducting desolvation and drying operationsconventionally well-known in the production of the modified conjugateddiene-based polymer. Also, when the compound Y contains the protectedprimary amino group, it is preferable to conduct (3) a step ofhydrolyzing the secondary modified conjugated diene-based polymer todeprotect the protected primary amino group derived from the compound Yafter the completion of the step (1) and step (2). Thus, the modifiedconjugated diene-based polymer having the primary amino group isobtained, which can be used as a modified conjugated diene-based polymerin the above rubber composition. Moreover, the usual method can be usedin the hydrolysis.

EXAMPLES

The following examples are given in illustration of the invention andare not intended as limitations thereof.

(Polymer A)

Into an autoclave of 5 L purged with nitrogen are charged 2.4 kg ofcyclohexane and 300 g of 1,3-butadiene in a nitrogen atmosphere. Intothe autoclave is charged a catalyst composition, which is previouslyprepared by reacting and maturing a solution of neodymium versatate(0.09 mmol) in cyclohexane, a solution of methylalumoxane (hereinafterreferred to as “MAO”)(3.6 mmol) in toluene, a solution of hydrogenateddiisobutylaluminum (hereinafter referred to as “DIBAH”) (5.5 mmol) anddiethylaluminum chloride (0.18 mmol) in toluene and 1,3-butadiene (4.5mmol) as a catalyst component at 40° C. for 30 minutes, and thenpolymerization is carried out at 60° C. for 60 minutes. The reactionconversion of 1,3-butadiene is approximately 100%. The resulting polymersolution is placed into a solution of methanol containing 0.2 g of2,4-di-tert-butyl-p-cresol to stop polymerization, and thereafter thesolvent is removed by steam stripping and the drying is conducted onrolls at 110° C. to obtain an unmodified polymer A (conjugateddiene-based polymer). As measured by the following method, the thusobtained polymer A has a Mooney viscosity [ML₁₊₄ (100° C.)] of 18, amolecular weight distribution (Mw/Mn) of 2.2, a cis-1,4 bond content of96.3% and a 1,2-vinyl bond content of 0.64%.

(1) Mooney Viscosity [ML₁₊₄ (100° C.)]

It is measured according to JIS K6300 with a L rotor under conditionsthat a preheating time is 1 minute and an operating time of the rotor is4 minutes and a temperature is 100° C.

(2) Molecular Weight Distribution (Mw/Mn)

It is measured through a gel permeation chromatography (trade name“HLC-8120GPC”, made by Toso Co., Ltd.) with a differential refractometeras a detector under the following conditions and calculated as aconversion value to standard polystyrene.

Column: two columns of trade name “GMHHXL” (made by Toso Co., Ltd.)

Column temperature: 40° C.

Mobile phase: tetrahydrofuran

Flow rate: 1.0 ml/min

Sample concentration: 10 mg/20 ml

(3) Microstructure [cis-1,4 Bond Content (%), 1,2-vinyl Bond Content(%)]

It is measured by an infrared method (Morello method) using a Fouriertransform infrared spectrophotometer (trade name “FT/IR-4100”, made byNippon Bunkosha Co., Ltd).

(Polymer B)

After polymerization is carried out in the same manner as in theproduction example of the polymer A, the polymer solution is furtherkept at a temperature of 60° C. and a solution of polymethylenepolyphenyl polyisocyanate (trade name “PAPI*135”, made by Dow ChemicalJapan Co., Ltd.) (hereinafter referred to as “cMDI”) (4.16 mmol asconverted isocyanate group (NCO)) in toluene is added to conductreaction (primary modification reaction) for 15 minutes. Subsequently, asolution of hexamethylene diamine ((hereinafter referred to as “HMDA”)(2.08 mmol) in toluene is added to conduct reaction (secondarymodification reaction) for 15 minutes. Thereafter, the reaction productis placed in a methanol solution containing 1.3 g of2,4-di-tert-butyl-p-cresol to stop polymerization, and then the solventis removed by steam stripping and the drying is conducted on roll at110° C. to obtain a polymer B (modified conjugated diene-based polymer).As measured by the above-mentioned method, the thus obtained polymer Bhas a Mooney viscosity [ML₁₊₄ (100° C.)] of 35, a molecular weightdistribution (Mw/Mn) of 2.3, a cis-1,4 bond content of 96.2% and a1,2-vinyl bond content of 0.59%.

(Polymer C)

After polymerization is carried out in the same manner as in theproduction example of the polymer A, the polymer solution is furtherkept at a temperature of 60° C. and a solution of4,4′-bis(diethylamino)benzophenone (2.08 mmol) in toluene is added toconduct reaction for 15 minutes. Thereafter, the reaction product isplaced in a methanol solution containing 1.3 g of2,4-di-tert-butyl-p-cresol to stop polymerization, and then the solventis removed by steam stripping and the drying is conducted on roll at110° C. to obtain a polymer C. As measured by the above-mentionedmethod, the thus obtained polymer C has a Mooney viscosity [ML₁₊₄ (100°C.)] of 24, a molecular weight distribution (Mw/Mn) of 2.0, a cis-1,4bond content of 96.0% and a 1,2-vinyl bond content of 0.58%.

(Polymer D)

After polymerization is carried out in the same manner as in theproduction example of the polymer A, the polymer solution is furtherkept at a temperature of 60° C. and a solution of trimethylolpropanetris[(3-(1-aziridinyl))propionate] (2.08 mmol) in toluene is added toconduct reaction for 15 minutes. Thereafter, the reaction product isplaced in a methanol solution containing 1.3 g of2,4-di-tert-butyl-p-cresol to stop polymerization, and then the solventis removed by steam stripping and the drying is conducted on roll at110° C. to obtain a polymer D. As measured by the above-mentionedmethod, the thus obtained polymer D has a Mooney viscosity [ML₁₊₄ (100°C.)] of 33, a molecular weight distribution (Mw/Mn) of 2.2, a cis-1,4bond content of 96.3% and a 1,2-vinyl bond content of 0.62%.

(Polymer E)

A glass bottle of about 1 liter volume provided with a rubber plug isdried and purged with nitrogen, and a solution of dried and purifiedbutadiene in cyclohexane and a dried cyclohexane are charged into theglass bottle purged with nitrogen, respectively, at a state of charging400 g of the cyclohexane solution of butadiene (butadiene concentration:12.0 mass %). Then, 0.30 mL of tert-butyllithium (1.57 M) and 0.185 mLof 2,2-di(2-tetrahydrofuryl)propane (0.2 N) are added to conductpolymerization in a water bath of 50° C. for 1.5 hours. Further, thepolymer solution is kept at a temperature of 50° C. and added with cMDI(0.84 mmol as converted to isocyanate group (NCO)) to conduct reactionfor 15 minutes, and thereafter reacted with HDMA (0.42 mmol).Thereafter, the reaction product is placed in a methanol solutioncontaining 1.3 g of 2,4-di-tert-butyl-p-cresol to stop polymerization,and then the solvent is removed by steam stripping and the drying isconducted on roll at 110° C. to obtain a polymer E. As measured by theabove-mentioned method, the thus obtained polymer E has a Mooneyviscosity [ML₁₊₄ (100° C.)] of 42, a molecular weight distribution(Mw/Mn) of 1.70, a cis-1,4 bond content of 45.1% and a 1,2-vinyl bondcontent of 18.33%.

(Polymer F)

After polymerization is carried out in the same manner as in theproduction example of the polymer A, the polymer solution is furtherkept at a temperature of 60° C. and a solution of1-trimethylsilyl-2-methylchloro-1-aza-2-silacyclopentane (2.08 mmol) intoluene is added to conduct reaction for 15 minutes. Thereafter, thereaction product is placed in a methanol solution containing 1.3 g of2,4-di-tert-butyl-p-cresol to stop polymerization, and then the solventis removed by steam stripping and the drying is conducted on roll at110° C. to obtain a polymer F (modified conjugated diene-based polymer).As measured by the above-mentioned method, the thus obtained polymer Fhas a Mooney viscosity [ML₁₊₄ (100° C.)] of 26, a molecular weightdistribution (Mw/Mn) of 2.1, a cis-1,4 bond content of 96.4% and a1,2-vinyl bond content of 0.62%.

Next, a rubber composition is prepared according to a compounding recipeshown in Table 1 and vulcanized at 145° C. for 33 minutes to obtain avulcanized rubber, and the resistance to crack growth and low heatbuildup (3% tan δ) thereof are measured by the following methods. Theresults are shown in Tables 2-3.

(4) Resistance to Crack Growth

A crack of 0.5 mm is formed in a central portion of a test specimen ofJIS No. 3 and fatigue is repeatedly applied thereto at room temperatureunder a strain of 50-100% to measure the repeat number until the sampleis cut. The values at each strain are measured and an average valuethereof is used. In Table 2, examples and comparative examplescompounded with carbon black having same nitrogen adsorption specificsurface area are represented by an index on the basis that a comparativeexample compounded with the polymer A is 100. In Table 3. it isrepresented by an index on the basis that Comparative Example 1 is 100.The larger the index value, the better the resistance to crack growth.

(5) Low Heat Buildup (3% tan δ)

It is measured using a dynamic spectrometer (made by RheometricCorporation in USA) under conditions that a tensile dynamic strain is3%, a frequency is 15 Hz and a temperature is 50° C. In Table 2,examples and comparative examples compounded with carbon black havingsame nitrogen adsorption specific surface area are represented by anindex on the basis that a comparative example compounded with thepolymer A is 100. In Table 3. it is represented by an index on the basisthat Comparative Example 1 is 100. The smaller the index value, thebetter the low heat buildup (low loss factor).

TABLE 1 Compounding substances parts by mass First stage polymer *1 50.0(non-productive natural rubber (NR) 50.0 mixing stage) carbon black *250.0 stearic acid 2.0 antioxidant 6C *3 3.5 Second stage zinc oxide 3.0(productive mixing antioxidant *4 1.0 stage) vulcanization acceleratorCZ-G *5 0.4 vulcanization accelerator DM-P *6 0.2 sulfur 1.4 *1 PolymersA-F, kind of polymer used is shown in Tables 2-3 *2 Nitrogen adsorptionspecific surface area of carbon black used is shown in Tables 2-3 *3N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylene diamine *4 Nocrac 224, madeby Ouchi Shinko Chemical Industrial Co., Ltd. *5N-cyclohexyl-2-benzothiazolyl sulfenamide *6 di-2-benzothiazolyldisulfide

TABLE 2 Comparative Comparative Comparative Comparative Example 1Example 1 Example 2 Example 2 Example 3 Example 3 Example 4 Example 4Nitrogen 42 42 78 78 145 145 42 42 adsorption specific surface area(N₂SA) of carbon black (m²/g) Kind of Polymer A Polymer B Polymer APolymer b Polymer A Polymer B Polymer E Polymer F polymer cis-1,4 bond96.3 96.2 96.3 96.2 96.3 96.2 45.1 96.4 content (%) vinyl bond 0.63 0.590.63 0.59 0.63 0.59 18.33 0.62 content (%) Resistance to 100 124 100 118100 104 75 121 crack growth (index) 3% tan δ 100 68 100 71 100 89 65 69(index)

As seen from the results of Table 2, the rubber compositions of Examples1-4 each compounded with a modified conjugated diene-based polymerhaving a cis-1,4 bond content of not less than 90%, a vinyl bond contentof not more than 1.2% and a primary amino group can largely improve theresistance to crack growth and low heat buildup as compared with therubber compositions of Comparative Examples 1-3 each compounded with amodified conjugated diene-based polymer having a cis-1,4 bond content ofnot less than 90% and a vinyl bond content of not more than 1.2% buthaving no primary amino group. Also, as seen from the results ofExamples 1-4, the effect of improving the resistance to crack growth andlow heat buildup can be largely improved when carbon black having anitrogen adsorption specific surface area of 20-180 m²/g is compounded.Moreover, in the rubber composition of Comparative Example 4, thecis-1,4 bond content of the polymer E compounded is low, so that theresistance to crack growth is largely deteriorated though the low heatbuildup is improved.

TABLE 3 Comparative Comparative Comparative Example 1 Example 5 Example6 Example 1 Nitrogen 42 42 42 42 adsorption specific surface area (N₂SA)of carbon black (m²/g) Kind of polymer Polymer A Polymer C Polymer DPolymer B cis-1,4 bond 96.3 96.0 96.3 96.2 content (%) vinyl bond 0.640.58 0.62 0.59 content (%) Modifying agent unmodified a *7 b *8 c *9Resistance to 100 107 108 124 crack growth (index) 3% tan δ (index) 10087 85 68 *7 4,4′-bis(diethylamino)benzophenone *8 trimethylolpropanetris[3-(1-aziridinyl)propionate] *9 cMDI (primary modification reaction)and HMDA (secondary modification reaction)

As seen from The results of Table 3, the rubber composition of Example 1compounded with the polymer B having a primary amino group introducedcan largely improve the resistance to crack growth and low heat buildupas compared with the rubber composition of Comparative Example 5 or 6compounded with the polymer C or D having a tertiary amino groupintroduced.

Next, a vulcanized rubber is obtained in the same manner as mentionedabove except that the amount of carbon black compounded in thecompounding recipe of Table 1 is changed, and the resistance to crackgrowth and low heat buildup thereof are measured by the above-mentionedmethods. The results are shown in Table 4.

In Table 4 is shown the amount of carbon black compounded per 100 partsby mass of the rubber component (polymer and natural rubber). Also, theresistance to crack growth and low heat buildup (3% tan δ) arerepresented in the examples having the same amount of carbon blackcompounded by an index on the basis that the comparative examplecompounded with the polymer A is 100.

TABLE 4 Comparative Comparative Example 7 Example 5 Example 8 Example 6Nitrogen 42 42 42 42 adsorption specific surface area (N₂SA) of carbonblack (m²/g) Amount of carbon 10 10 90 90 black compounded per 100 partsby mass of rubber component (part by mass) Kind of polymer Polymer APolymer B Polymer A Polymer B cis-1,4 bond 96.3 96.2 96.3 96.2 content(%) vinyl bond content 0.63 0.59 0.63 0.59 (%) Resistance to crack 100110 100 123 growth (index) 3% tan δ (index) 100 78 100 73

As seen from the results of Table 4, the effect of improving theresistance to crack growth and low heat buildup can be largely improvedwhen the amount of carbon black compounded per 100 parts by mass of therubber component is within a range of 10-100 parts by mass.

The invention claimed is:
 1. A method of producing a modified conjugateddiene-based polymer, characterized by comprising: (1) a step of reactinga conjugated diene-based polymer having a cis-1,4 bond content of notless than 90% and a vinyl bond content of not more than 1.2% and anactive terminal with a compound X having a functional group A indicatinga reactivity to the active terminal and at least one reactive functionalgroup B (provided that the functional group A and the functional group Bmay be same) to obtain a primary modified conjugated diene-basedpolymer; and (2) a step of reacting the primary modified conjugateddiene-based polymer with a compound Y having a functional group Cindicating a reactivity to the reactive functional group B and at leastone primary amino group or protected primary amino group (provided thatthe functional group C may be the primary amino group or the protectedprimary amino group) to obtain a secondary modified conjugateddiene-based polymer.
 2. A method of producing a modified conjugateddiene-based polymer according to claim 1, wherein the conjugateddiene-based polymer has a vinyl bond content of not more than 0.8%.
 3. Amethod of producing a modified conjugated diene-based polymer accordingto claim 1, which further comprises (3) a step of hydrolyzing thesecondary modified conjugated diene-based polymer to deprotect theprotected primary amino group derived from the compound Y.
 4. A methodof producing a modified conjugated diene-based polymer according toclaim 1, wherein the conjugated diene-based polymer is synthesized witha rare earth metal as a catalyst.
 5. A method of producing a modifiedconjugated diene-based polymer according to claim 1, wherein thecompound X is polymethylene polyphenyl polyisocyanate and the compound Yis hexamethylene diamine.
 6. A modified conjugated diene-based polymerproduced by a method as claimed in claim 1.